Physics

Today I read with pleasure a paper on Supersymmetry which is surprisingly well written and clear. I can only warmly advise anybody seriously interested in the phenomenology of SUSY (in particular, the version called "constrained minimal supersymmetric extension of the Standard Model", cMSSM for friends) to give it a close look. The cMSSM is a very attractive "minimal" option to extend the Standard Model with a minimal addition of parameters (still, quite a few, as in any Supersymmetric theory). Its appeal lies in the fact that one may basically study the resulting predicted phenomenology by…

The family of Upsilon resonances is among the few things that can always cheer me up and remind me about my fascination for elementary particles when I get bored about my job. The sight of their mass peaks implies that heavy quarks bind together exactly as electrons and positrons do, orbiting around one another for a brief instant of time. An impossibly brief one, and yet quite long for subnuclear standards. It is always a refreshing and inspiring sight (below, see the three lowest-lying Upsilon states as they are seen by the CDF experiment at the Fermilab Tevatron collider, in a sizable…

Since 1930, efforts have been made to get our best theory for gravity - general relativity (GR) - to work with our best theory for atoms - quantum field theory (QFT) in the forms quantum electrodynamics (QED) and quantum chromodynamics (QCD).  In this comparatively short blog, I will frame the struggle and let people provide their own speculations in the comments (mine will reside there too, so it will be easy to skip if you would like :-) Consider three physicists: Feynman, Weinberg, and Hawking. All are so far better in depth and breadth of their understanding of general relativity…

This week's graph comes from a recent publication by the CMS experiment, the one I am a proud member of together with about 3000 colleagues from all over the world. CMS (see a 3-D sketch below) is one of the two huge detectors collecting the faint signals of particles produced in the powerful 8-TeV proton-proton collisions delivered by the CERN Large Hadron Collider. The CMS experiment has recently been publishing one by one the results of many largely independent searches for Supersymmetric particles in the data collected during 2011; not surprising to sceptics like me, these results are…

The medium in which light propagates is space. This space can curve. The curvature is not static. So, this space moves. Its behavior can be analyzed by a kind of fluid dynamics. Let us call this method quantum fluid dynamics. It differs from conventional fluid dynamics in the medium that is treated. In conventional fluid dynamics this is a gas or a fluid. Fluid dynamics concerns density distributions and currents. In quantum fluid dynamics these are space density distributions and space current density distributions. They can be combined in quaternionic distributions, where the real part…

Entropy. A subject that comes back again and again and again and again and again in this blog. And so does the question in my inbox: "what exactly is entropy?" On the internet you can find a plethora of answers to this question. The quality of the answers ranges from 'plain nonsense' to 'almost right'. The correct definition of entropy is the one given in a previous blog: "the entropy of a physical system is the minimum number of bits you need to fully describe the detailed state of the system" So forget about statements like "entropy is disorder", "entropy measures randomness" and all…

At about the 1 minute mark in a youtube Yale Lecture, titled The Taylor Series and Other Mathematical Concepts, the teacher tells his class that he will be presenting the Taylor Series and the class erupts into laughter.  Why? As an undergraduate, I vaguely recall my dissatisfaction with Taylor's Theorem. It says that, for a well behaved function f(x), A.   [It takes other forms depending on conventions. For example, the few sites I've checked set x=0 and let h be the parameter and call it x. B.  There is also a Remainder Term that involves an integral that, following…

[Retracted: In this blog I hope to get to a well known issue in general relativity, namely that gravitational energy needs to be defined for a spacetime volume instead of at a point.]  The [new] goal is to sketch the Riemann curvature tensor...There are limitations to what one can do in a blog.  The flowchart is from Sean Carroll's lecture notes that I highly recommend.  In this blog, I will presume I am working with a Riemannian manifold, the final step of the geometry construction.  A Riemannian manifold allows one to do differential calculus even in curved spacetime.…

Researchers have discovered a previously unknown particle composed of three quarks in the Large Hadron Collider (LHC) particle accelerator. The baryon known as Xi_b^* confirms fundamental assumptions of physics regarding the binding of quarks.  The baryon family refers to particles that are made up of three quarks and quarks form a group of six particles that differ in their masses and charges. The two lightest quarks, “up” and “down” quarks, form the two atomic components, protons and neutrons. All baryons that are composed of the three lightest quarks (“up”, “down” and “strange” quarks…

In a recent PRL article Artemis Spyrou and collaborators have reported on the first observation of an exotic form of nucleons, the long-sought dineutron. Dineutron was predicted theoretically as a short-lived bound state of two neutrons emitted from a nucleus. The formation is possible due to the strong nuclear force that may hold the two neutrons close by for some time. The dineutron is not easy to get. You have to find it as a decay product in some rare decay of an exotic, almost unbound nucleus under at least one special requirement: the nucleus emitting the dineutron should show a larger…